This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2001-204435 filed in JAPAN on Jul. 5, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel cell type reactor and a method for producing a chemical compound by using the reactor. More particularly, the present invention is concerned with a fuel cell type reactor for performing an oxidation reaction of a system comprising a substrate, a reductant and an oxidant, comprising: a casing; an anode which comprises an anode active material and which is ion-conductive or active species-conductive; and a cathode which comprises a cathode active material and which is ion-conductive or active species-conductive, wherein the anode and the cathode are disposed in spaced relationship in the casing to partition the inside of the casing into an intermediate compartment between the anode and the cathode, an anode compartment on the outside of the anode and a cathode compartment on the outside of the cathode. The reactor of the present invention can be used for producing various chemical compounds which are useful in the chemical industry. The present invention is also concerned with a method for producing a chemical compound by performing an oxidation reaction, using the reactor of the present invention. The reactor of the present invention can be applied to various oxidation reactions, and is especially useful for performing selective oxidation reactions, for example, partial oxidation of an alkane, partial oxidation of an alcohol, epoxidation of an olefin, hydroxylation of an aromatic compound, partial oxidation of an amine and partial oxidation of a ketone. By using the reactor of the present invention, various chemical compounds having high values added thereto can be produced directly from a low-priced oxidant (such as oxygen), a reductant and a substrate, without using an expensive oxidizing agent, such as hydrogen peroxide or an organic or an inorganic peroxide. The reactor of the present invention is also applicable to various oxidative addition reactions, for example, a carbonylation reaction of an alcohol, a phenolic compound or an olefin; the Wacker reaction of an olefin; an acetoxylation reaction, oxychlorination reaction or coupling reaction of an olefin or an aromatic compound; and an esterification reaction of an alcohol. The reactor enables efficient and stable production of useful chemical compounds. For example, by using the reactor of the present invention, t-butylhydroperoxide can be synthesized in a single step by a selective oxidation reaction, from oxygen, t-butanol and hydrogen. t-Butyl-hydroperoxide is a useful chemical compound which is used as an oxidizing agent, a polymerization initiator, a curing agent and a desiccant in the chemical, pharmaceutical and food industries and the like.
2. Prior Art
Conventionally, oxidation reactions which are well known in the industry, especially a selective oxidation reaction and an oxidative addition reaction, have been carried out by employing the techniques as described below.
Useful chemical compounds can be efficiently produced under moderate conditions with high selectivity by performing a selective oxidation reaction, using an oxidizing agent (such as hydrogen peroxide or an organic or an inorganic peroxide) which can produce an active oxygen species (an electrophilic oxygen species) having high chemical potential (see, for example, xe2x80x9cShin Jikken Kagaku Koza 15, Sanka to Kangen I-2 (New Lecture on Experimental Chemistry 15, Oxidation and Reduction, I-2)xe2x80x9d, edited by Japan Chemical Society, p. 605, 1976, Japan; and xe2x80x9cCatalytic Oxidations with Hydrogen Peroxide as Oxidantxe2x80x9d, G. Strukul, Kluwer Academic Publishers, 1992, the Netherlands). Examples of selective oxidation reactions include oxidation of an alkane, oxidation of an alcohol, epoxidation of an olefin, oxidation or ammoximation of a ketone, oxidation of an aldehyde, oxidation of an ether, hydroxylation of an aromatic compound, oxidation of an amine and oxidation of a sulfur compound.
The xe2x80x9cselective oxidation reactionxe2x80x9d mentioned herein means a reaction which proceeds in the presence of an electrophilic oxygen species, such as the selective oxidation reactions mentioned in the above-mentioned documents.
On the other hand, it is well known that, as a conventional method for producing hydrogen peroxide, which is a useful oxidizing agent as mentioned above, an autoxidation reaction using alkylanthraquinone is commercially used (see xe2x80x9cKagaku Binran, Oyo-kagaku-hen I (Chemical Handbook, Applied Chemistry I)xe2x80x9d, edited by Japan Chemical Society, p. 302, 1986, Japan). However, the conventional method for producing hydrogen peroxide is economically disadvantageous not only in that the method requires a large amount of an organic solvent and but also in that, due to the generation of various by-products and degradation of a catalyst, the method requires various additional steps for separation of by-products and for regeneration of the degraded catalyst. Therefore, it has been desired to develop a production method by which hydrogen peroxide can be produced at a low cost, as compared to the case of the conventional method.
In addition, as a useful organic peroxide, t-butylhydroperoxide is also known. Conventionally, t-butylhydroperoxide has been produced, for example, by a method in which t-butanol or isobutylene as a substrate, namely a raw material, is reacted with a strong acid, such as sulfuric acid, and hydrogen peroxide (see, for example, xe2x80x9cYuki-Kasankabutsu (Organic Peroxides)xe2x80x9d, edited by the Organic Peroxide Research Group, p. 220, 1972, Japan). However, the conventional method is disadvantageous from the viewpoint of economy and safety; specifically, the conventional method has disadvantages in that hydrogen peroxide (which is expensive) is necessary, and the raw material is reacted with a liquid mixture of a high concentration aqueous sulfuric acid (60 to 70 wt %) and a high concentration aqueous hydrogen peroxide (30 to 50 wt %).
For these reasons, from the practical and commercial viewpoint, it has been desired to develop a method by which various types of selective oxidation reactions can be performed by directly oxidizing a substrate with oxygen in the presence of a catalyst without using an expensive oxidizing agent, such as hydrogen peroxide. For example, a method for producing phenol directly from benzene and oxygen in the presence of a catalyst has long been studied. However, the reaction method which has been studied has the following problems. First, a high temperature is necessary for the reaction. Further, although various types of catalysts can catalyze the reaction, many of such catalysts pose a problem in that the reaction system containing such catalysts causes phenol as a reaction product to have higher reactivity than benzene as a substrate, so that, although the reaction rate of benzene can be increased, the selectivity for phenol is decreased. Thus, no method which is commercially employable has been developed. With respect not only to such reaction system (which causes phenol as a reaction product to have higher reactivity than benzene) but also to other oxidation reactions using oxygen, great efforts have been made for increasing the selectivity for a desired reaction product. However, there is no method which is satisfactory from the viewpoint of economy and safety. It is considered that the reason why such an oxidation reaction using oxygen does not proceed with high selectivity for a desired product is because, when oxygen molecules are activated by a catalyst, an electron transfer from the catalyst to the oxygen molecules inevitably occurs, so that oxygen molecules are mainly converted to nucleophilic oxygen anion active species, making it difficult for an electrophilic addition reaction to proceed (see Catalysis Today, 45, 3-12, 1998, the U.S.A.).
In recent years, in order to alleviate the above-mentioned problems, studies on a new method have been made for synthesizing a chemical compound, in which a catalyst system which is similar to a biological catalyst system is used. Monooxygenase, which is an enzyme present in the living body, activates an oxygen molecule by utilizing the reducing ability of NADPH. In imitation of this mechanism, in the synthetic chemistry, a method can be used in which oxygen and a reducing agent, such as hydrogen, carbon monoxide or aldehyde, are contacted with each other in the presence of a catalyst system, thereby generating an active oxygen species under moderate conditions. In this case, since energy necessary to cleave an oxygen bond is supplied through the oxidation of the reducing agent, an electrophilic active oxygen species can be selectively generated without using a large amount of energy. The present inventors previously proposed a method for producing phenol, comprising contacting oxygen, benzene and hydrogen with each other in the presence of an Eu-Ti-Pt catalyst (see xe2x80x9cDai 84-kai Shokubai Toronkai Yokou-shu 3F20 (the preliminary text for the 84th Forum on Catalysts, 3F20)xe2x80x9d, 1999, Japan). According to this method, phenol can be produced with high selectivity under moderate conditions from benzene and oxygen in a single step. With respect to the reaction in this method, it is presumed that oxygen undergoes partial reduction by hydrogen on the surface of the catalyst and is converted to an active oxygen species, which is effective for the hydroxylation of benzene, thereby exhibiting improved selectivity for phenol. However, this method has problems in that there is a great danger of explosion due to the presence of hydrogen, and the utility of hydrogen is low. In addition to this method, there are also known methods similar thereto, such as a method for producing phenol, comprising contacting oxygen, benzene and hydrogen with each other in the presence of a Ptxe2x80x94V2O5/SiO2 catalyst (Appl. Catal., A, 131, 33, 1995, U.S.A.); a method for producing cyclohexene oxide, comprising contacting oxygen, cyclohexene and hydrogen in the presence of an Mn complex/Pt colloidal catalyst (J. Am. Chem. Soc., 101, 6456, 1979, U.S.A.); and a method for producing propylene oxide from propylene, for producing acetone from propane or for producing t-butanol from isobutane, which comprises subjecting a substrate to a gaseous phase oxidation with oxygen in the presence of hydrogen and an Au/TiO2 catalyst (xe2x80x9cShokubai (Catalyst)xe2x80x9d, Vol. 37, No.2, 72, 1995, Japan). However, each of these methods has problems similar to the above-mentioned problems, and hence cannot be commercially practically employed.
Besides the selective oxidation reaction, the oxidative addition reaction is also known as a useful reaction in the chemical industry. The xe2x80x9coxidative addition reactionxe2x80x9d mentioned herein means a condensation reaction of at least one chemical compound in the presence of oxygen. Examples of compounds to be condensed include various organic and inorganic compounds, such as an olefin, a diene, an alcohol, a phenolic compound, an aromatic compound, water, carbon monoxide, hydrogen halogenide, acetic acid and prussic acid. The oxidative addition reaction covers a wide variety of types of reactions.
By the oxidative addition reaction, useful chemical substances can be produced. Representative examples of oxidative addition reactions include carbonylation of an alcohol for synthesizing a dialkyl carbonate, carbonylation of a phenolic compound for synthesizing a diaryl carbonate, carbonylation of an olefin for synthesizing an ester, carbonylation of an olefin for synthesizing an unsaturated acid, and the Wacker reaction of an olefin for synthesizing an aldehyde or a ketone. Each of these reactions is performed in the presence of oxygen and a catalyst comprising an element (such as palladium) selected from the elements of the Groups 8, 9, 10 and 11 of the Periodic Table. Besides the above-mentioned reactions, there are also known other oxidative addition reactions, such as acetoxylation, oxychlorination and oxycyantion of an olefin or an aromatic compound, a coupling reaction of an olefin or an aromatic compound, and esterification of an alcohol. Thus, the oxidative addition reaction is highly useful in the organic chemical industry (see, for example, xe2x80x9cShokubai Koza Vol.8 (Kogyo Shokubai Hanno-hen 2), Kogyo Shokubai Hanno I (Lecture on Catalysts Vol.8 (Commercial Catalytic Reactions No.2), Commercial Catalytic Reactions I)xe2x80x9d, edited by Japan Catalyst Society, p. 196, 1985, Japan).
However, these many oxidative addition reactions have problems in that a lowering of the catalyst activity occurs during the reaction, that a corrosion of a reactor occurs due to a by-produced, chlorine-containing compound derived from a catalyst, that a large amount of energy is consumed due to the use of high reaction temperature and high reaction pressure, that a danger of explosion is present due to the mixing of a substrate and oxygen, and that the selectivity for and yield of a desired compound are low.
On the other hand, in recent years, studies have been made for producing a useful chemical compound under moderate conditions by using a fuel cell system. A fuel cell is a system which is intended to perform a process in which a fuel is electrochemically reacted with an oxidant through a diaphragm containing an electrolyte solution, thereby effecting an electrochemical complete combustion of the fuel, and a free energy change occurring during the electrochemical reaction is directly converted to electrical energy. In the operation of a fuel cell, an electron discharge reaction and an electron accepting reaction are, respectively, effected at an anode and a cathode which are connected to each other through an electron-conductive material in the outside of the fuel cell to form an external circuit, and a flow of electrons through the external circuit is obtained as an electric power. When a fuel cell is regarded as a chemical reactor for use in an organic synthesis, the reactor is a device which is capable, in principle, of both producing a useful chemical compound and providing electricity.
A method for effecting an organic synthesis by using a fuel cell system has the below-mentioned features 1) to 4), which are advantageous for commercial production of chemical compounds.
1) Since an active species can be separated and a special reaction zone can be formed, it becomes possible to perform a selective reaction, which is difficult to perform by an ordinary catalytic reaction.
2) The reaction rate and the selectivity can be easily electrically controlled.
3) When the external circuit is loaded, electricity can be obtained in addition to a desired chemical compound.
4) Since an oxidant, such as oxygen, and a reductant, such as hydrogen, are separated from each other by a diaphragm disposed therebetween, the danger of an explosion can be decreased.
Examples of selective oxidation reactions and oxidative addition reactions which are performed using a fuel cell system are as follows. Examples of selective oxidation reactions which are performed using a fuel cell system include (I) a hydroxylation reaction of benzene (Electrochimica Acta, Vol. 39, No. 17, 2545, 1994, Switzerland) and (II) a partial oxidation reaction of an alkane (J. Chem. Soc. Faraday Trans., 90(3), 451, 1994, England). Examples of oxidative addition reactions which are performed using a fuel cell system include (III) a carbonylation reaction of methanol (Electrochimica Acta, Vol. 39, No. 14, 2109, 1994, Switzerland) and (IV) the Wacker reaction of an ethylene (J. Chem. Soc., Chem. Commun., 1988, England).
For example, each of the fuel cell type reactors used in the above-mentioned documents (I), (III) and (IV) comprises a casing, an ion-conductive diaphragm (containing an electrolyte solution), an anode and a cathode, wherein the ion-conductive diaphragm is sandwiched between the anode and the cathode to form a laminate structure, and wherein the laminate structure is disposed in the middle of the inside of the casing to partition the inside of the casing into an anode compartment on the outside of the anode and a cathode compartment on the outside of the cathode. In operation, a substrate in the gaseous form is supplied to either the anode compartment or the cathode compartment. In addition, a reductant and an oxidant both in the gaseous form are, respectively, supplied to the anode compartment and the cathode compartment. A desired product is produced in the compartment where the substrate is supplied. In the document (I), benzene and oxygen both in the gaseous form are supplied to the cathode compartment, and hydrogen is supplied to the anode compartment, and phenol is produced in the cathode compartment. In the document (III), methanol and carbon monoxide both in the gaseous form are supplied to the anode compartment, and oxygen is supplied to the cathode compartment, and dimethyl carbonate is produced in the anode compartment. In the document (IV), ethylene and water both in the gaseous form are supplied to the anode compartment, and oxygen is supplied to the cathode compartment, and acetaldehyde is produced in the anode compartment. On the other hand, the fuel cell type reactor used in the document (II) comprises a casing, an ion-conductive diaphragm (containing an electrolyte solution), an anode and a cathode, wherein the ion-conductive diaphragm is sandwiched between the anode and the cathode to form a laminate structure, and wherein the laminate structure is disposed in the middle of the inside of the casing to partition the inside of the casing into an anode compartment on the outside of the anode and a cathode compartment on the outside of the cathode. In operation, cyclohexane as a substrate in the liquid form is supplied to the cathode compartment, and oxygen in the gaseous form is also supplied into the liquid phase (substrate) of the cathode compartment, and hydrogen is supplied to the anode compartment, and cyclohexanol is produced in the liquid phase of the cathode compartment.
However, methods for producing a chemical compound by using the above-mentioned conventional fuel cell type reactors have problems in that there is a danger of an explosion due to the reaction of a substrate and an oxidant, and there is a possibility of formation of a by-product due to a side reaction between a desired reaction product and an oxidant. Further, with respect to the method of the document (II) wherein oxygen in the gaseous form is blown into a liquid phase composed of a substrate, problems arise in that oxygen exhibits a poor solubility in the liquid phase (substrate) and hence the reaction rate becomes low and that the concentration of the desired reaction product in the liquid phase cannot become high.
Besides the studies shown in the above-described documents (I) to (IV), various other studies for applying a fuel cell system to a chemical synthesis have been reported in other documents. However, such other documents disclose reactors having a structure which is essentially the same as in the documents (I) to (IV), and such other documents disclose methods for producing a chemical compound by using the reactors respectively disclosed therein. Therefore, the teachings of such other documents are nothing more than the teachings of the documents (I) to (IV).
In this situation, the present inventors have made extensive and intensive studies with a view toward solving the above-mentioned problems of the prior art. As a result, it has unexpectedly been found that this objective can be attained by using a fuel cell type reactor for performing an oxidation reaction of a system comprising a substrate, a reductant and an oxidant, comprising: a casing; an anode which comprises an anode active material and which is ion-conductive or active species-conductive; and a cathode which comprises a cathode active material and which is ion-conductive or active species-conductive, wherein the anode and the cathode are disposed in spaced relationship in the casing to partition the inside of the casing into an intermediate compartment between the anode and the cathode, an anode compartment on the outside of the anode and a cathode compartment on the outside of the cathode, and wherein the intermediate compartment has an inlet for an electrolyte solution and a substrate, the anode compartment has an inlet for a reductant, and the cathode compartment has an inlet for an oxidant. That is, it has surprisingly been found that, by using the above-mentioned reactor for performing an oxidation reaction, various useful chemical compounds can be produced efficiently, safely and stably from a substrate, a reductant and an oxidant. The present invention has been completed, based on this novel finding.
Accordingly, it is an object of the present invention to provide a fuel cell type reactor for performing an oxidation reaction of a system comprising a substrate, a reductant and an oxidant, wherein the fuel cell type reactor can be used for producing various useful chemical compounds efficiently, safely and stably by the oxidation reaction.
It is another object of the present invention to provide a method for producing various useful chemical compounds efficiently, safely and stably, which comprises performing an oxidation reaction of a system comprising a substrate, a reductant and an oxidant by using the above-mentioned fuel cell type reactor.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.